A program of research is proposed to conduct basic behavioral and biobehavioral studies in mental retardation and intellectual development focusing upon the development of learning and symbolic processes, personality, and motivation, and upon the facilitation of learning and efficient performance in mentally retarded and nonretarded children. A major goal is to identify strategies for improving the performance characteristics of intellectually and educationally retarded persons. A second general objective is to contribute to theories of cognition, learning, and human development. The program is conducted in the Institute on Mental Retardation and Intellectual Development and is organized into three interrelated laboratories (research groups): the Laboratory on Symbolic Processes, the Laboratory on Intrinsic Motivation, and the Laboratory on Comparative Development. Among the specific problems to be investigated are the following: the ontogenesis of intrinsic motivation in infancy and early childhood; the development of curiosity, exploratory, and play behavior; the relationship of intrinsic motivation to learning and performance efficiency, including both laboratory and classroom studies; the structure of personality in both retarded and nonretarded children and personality characteristics of good and poor learners; reciprocal impact of developmentally delayed and developmentally advance sibling upon behavioral and physiological development; facilitation of learning as a function of endocrine status; the emotions as variables in learning and the development of social skills; emotion communication, and exploratory behavior; developmental and behavioral effects of responsive and nonresponsive rearing environments; variables that affect the recognition and understanding of linguistic and visually portrayed events; developmental interrelation of sensory, verbal, and imaginal system; difference in performance variability of retarded and nonretarded persons.